Cytokeratin 7 is the intermediate silk protein mainly expressed in epithelial cells. The heterodine of keratin consists of a polymerization filament by an acid -keratin (or type I keratin, keratin 9 to 23) and alkaline keratin (or type II keratin, keratin 1 to 8). Expression similar to but more limited than keratins 8 and 18 in simple, pseudostratified and ductal epithelium, mesothelium and urothelium. It's generally expressed (with some variation) in adenocarcinoma of lung, breast, thyroid, endometrium, cervix, ovary, salivary gland, upper GI tract, urothelial carcinoma, papillary renal cell carcinoma and Paget disease. It's generally negative (with some variation) in colorectal carcinoma, Merkel cell carcinoma, hepatocellular carcinoma, prostatic adenocarcinoma, adrenocortical tumors and squamous cell carcinoma.